Exploring microbial growth dynamics in a pilot-scale microalgae raceway fed with urban wastewater: Insights into the effect of operational variables.

Microalgae-based wastewater treatment is a promising technology efficient for nutrient recycling and biomass production. Studies continuously optimize processes to reduce costs and increase productivity. However, changes in the operational conditions affect not only biomass productivity but the dynamics of the overall microbial community. This study characterizes a microalgae culture from an 80 m2 pilot-scale raceway reactor fed with untreated urban wastewater. Operational conditions such as pH, dissolved oxygen control strategies (On-off, PI, Event-based, no control), and culture height were varied to assess microbial population changes. Results demonstrate that increased culture height significantly promotes higher microalgal and bacterial diversity. pH, dissolved oxygen and culture height highly affects nitrifying bacteria activity and nitrogen accumulation. Furthermore, the system exhibited high disinfection capability with average Logarithmic Reduction Values (LRV) of 3.36 for E. coli and 2.57 for Clostridium perfringens. Finally, the fungi species detected included Chytridiomycota and Ascomycota, while purple photosynthetic bacteria were also found in significant abundance within the medium.

Environmental micro-niche filtering shapes bacterial pioneer communities during primary colonization of a Himalayas' glacier forefield.

The pedogenesis from the mineral substrate released upon glacier melting has been explained with the succession of consortia of pioneer microorganisms, whose structure and functionality are determined by the environmental conditions developing in the moraine. However, the microbiome variability that can be expected in the environmentally heterogeneous niches occurring in a moraine at a given successional stage is poorly investigated. In a 50 m2 area in the forefield of the Lobuche glacier (Himalayas, 5050 m above sea level), we studied six sites of primary colonization presenting different topographical features (orientation, elevation and slope) and harbouring greyish/dark biological soil crusts (BSCs). The spatial vicinity of the sites opposed to their topographical differences, allowed us to examine the effect of environmental conditions independently from the time of deglaciation. The bacterial microbiome diversity and their co-occurrence network, the bacterial metabolisms predicted from 16S rRNA gene high-throughput sequencing, and the microbiome intact polar lipids were investigated in the BSCs and the underlying sediment deep layers (DLs). Different bacterial microbiomes inhabited the BSCs and the DLs, and their composition varied among sites, indicating a niche-specific role of the micro-environmental conditions in the bacterial communities' assembly. In the heterogeneous sediments of glacier moraines, physico-chemical and micro-climatic variations at the site-spatial scale are crucial in shaping the microbiome microvariability and structuring the pioneer bacterial communities during pedogenesis.

Growth Performance, Biochemical Composition and Nutrient Recovery Ability of Twelve Microalgae Consortia Isolated from Various Local Organic Wastes Grown on Nano-Filtered Pig Slurry.

This paper demonstrated the growth ability of twelve algae-microbial consortia (AC) isolated from organic wastes when a pig slurry-derived wastewater (NFP) was used as growth substrate in autotrophic cultivation. Nutrient recovery, biochemical composition, fatty acid and amino acid profiles of algae consortia were evaluated and compared. Three algae-microbial consortia, i.e., a Chlorella-dominated consortium (AC_1), a Tetradesmus and Synechocystis co-dominated consortium (AC_10), and a Chlorella and Tetradesmus co-dominated consortium (AC_12) were found to have the best growth rates (µ of 0.55 ± 0.04, 0.52 ± 0.06, and 0.58 ± 0.03 d-1, respectively), which made them good candidates for further applications. The ACs showed high carbohydrates and lipid contents but low contents of both proteins and essential amino acids, probably because of the low N concentration of NFP. AC_1 and AC_12 showed optimal ω6:ω3 ratios of 3.1 and 3.6, which make them interesting from a nutritional point of view.

Aridity modulates belowground bacterial community dynamics in olive tree.

Aridity negatively affects the diversity and abundance of edaphic microbial communities and their multiple ecosystem services, ultimately impacting vegetation productivity and biotic interactions. Investigation about how plant-associated microbial communities respond to increasing aridity is of particular importance, especially in light of the global climate change predictions. To assess the effect of aridity on plant associated bacterial communities, we investigated the diversity and co-occurrence of bacteria associated with the bulk soil and the root system of olive trees cultivated in orchards located in higher, middle and lower arid regions of Tunisia. The results indicated that the selective process mediated by the plant root system is amplified with the increment of aridity, defining distinct bacterial communities, dominated by aridity-winner and aridity-loser bacteria negatively and positively correlated with increasing annual rainfall, respectively. Aridity regulated also the co-occurrence interactions among bacteria by determining specific modules enriched with one of the two categories (aridity-winners or aridity-losers), which included bacteria with multiple PGP functions against aridity. Our findings provide new insights into the process of bacterial assembly and interactions with the host plant in response to aridity, contributing to understand how the increasing aridity predicted by climate changes may affect the resilience of the plant holobiont.

Air side-stream ammonia stripping in a thin film evaporator coupled to high-solid anaerobic digestion of sewage sludge: Process performance and interactions.

Air side-stream ammonia stripping in a thin-film evaporator (TFE) is proposed for the first time to control total ammonia nitrogen (TAN) concentration in a centralized full-scale plant performing high-solid anaerobic digestion (HSAD) of sewage sludge (SS). In this process, anaerobically digesting sludge (ADS) is continuously recirculated from the digester to the TFE unit where ammonia is stripped by an air stream. The stripped ammonia reacts with sulfuric acid in an absorption unit to produce ammonium sulfate. Overall, HSAD coupled to air side-stream ammonia stripping results in a twofold production of fertilizers (i.e. ammonium sulfate and SS digestate) recycling nutrients from organic wastes in agreement with the principles of circular economy. This study evaluates the influence of different operational airflow rates, temperatures and CO2 concentrations on air side-stream ammonia stripping in the TFE without alkali addition and the impact of air-based ammonia stripping on HSAD performance at full-scale. The study also investigates the chemistry and the interaction between the ammonia and carbonate subsystems of ADS and clarifies the stoichiometric relationship between ammonia and CO2 stripping.

Organic wastes/by-products as alternative to CO2 for producing mixotrophic microalgae enhancing lipid production.

In this work, white wine lees (WWL), cheese whey (CW), and glycerol (GLY) were used as carbon (C) sources to mixotrophically support the production of the microalga Nannochloropsis salina, replacing CO2 supply. In doing so, the alga was allowed to grow on C sources dosed at 2 g L-1, 3 g L-1, and 4 g L-1 of C, in the presence and absence of CO2 supply. WWL and CW were not able to support the algal growth due to a fungal contamination that was genomically identified, while GLY gave interesting results in particular with 3 g L-1 of C. GLY-C was able to replace CO2-C completely when the latter was omitted, showing an algal biomass production similar to those obtained in autotrophy. If CO2-C was provided jointly with GLY-C, biomass production and lipid contents increased more than 30% and 23%, respectively, compared to autotrophy.

Phosphatase activity and its relationship with physical and chemical parameters during vermicomposting of filter cake and cattle manure.

BACKGROUND: Recycling of phosphorus (P) from organic residues (ORs) is important to develop environmentally friendly agriculture. The use of this P source depends on phosphatase enzymes, which can be affected by a chain of parameters during maturation of ORs. In this study the phosphatase activity levels throughout vermicomposting of filter cake (FC) and cattle manure (CM) were correlated with different physical and chemical parameters in an effort to increase the knowledge about recycling of P from ORs. RESULTS: FC presented higher total nitrogen content (TNC), total organic carbon (TOC), humic acid (HA) content, water-soluble P (WSP), phosphatase activities and nanopore volume than CM during vermicomposting. Decreases in TOC of CM resulted from carbohydrate mineralization, which was not observed for FC. CM showed increased hydrophobic index during vermicomposting while FC showed a slight decrease. CONCLUSION: Phosphatase activities correlated positively with TOC, pH and WSP and negatively with HA content for both vermicomposts. Nanopore volume was negatively correlated with phosphatase activities for FC but not for CM. No correlations between hydrophobicity and phosphatase activities were found for FC. Increased hydrophobicity throughout vermicomposting of CM could be partially associated with decreases in phosphatase levels.

Ecotoxicological assessment of waste-derived organic fertilizers and long-term monitoring of fertilized soils using a multi-matrix and multi-species approach.

The present study investigates the ecotoxicity of 7 biofertilizers, including biowaste-derived organic matrices. Real-field tests were conducted to assess the impacts of soil fertilization with sewage sludge digestate from high-solid thermophilic anaerobic digestion (HSTAD) compared to those obtained on non-amended and urea-fertilized soils. The physical-chemical and ecotoxic impact of HSTAD digestate on soil was monitored for 12 months, at 5 time points and 2 soil depths, on a maize field divided in 3 portions (non-treated, fertilized with urea, amended with digestate). The chemical and physical characteristics of the soil were previously analyzed for 3 years to provide a long-term outlook of the impacts of biofertilizer application. Seven bioindicators were utilized for direct (on whole soil) and indirect (on soil elutriates) ecotoxicological tests on fertilizers and amended soils, including plant seeds (Lepidium sativum, Sorghum saccharatum, and Sinapsis alba), the aquatic organism Daphnia magna, the alga Raphidocelis subcapitata, the luminescent bacterium Aliivibrio fischeri, and the Nematode Caenorhabditis elegans. No serious negative effects on soil fertilized with HSTAD digestate were evidenced. Conversely, bioassays rather showed positive effects, encouraging the utilization of HSTAD digestate in agriculture, considering the proper concentrations of use. The obtained data were interpolated and a test battery integrated index was generated, confirming the absence of ecotoxicological risk for the soils amended with the applied fertilizers. The long-term evolution of the physical-chemical soil characteristics (including the concentrations of potential contaminants) was similar for both HSTAD digestate and urea application as well as for non-fertilized soil, indicating no negative effects due to digestate application on land. On the contrary, digestate application improved the content of stabilized organic matter and nutrients in soil. This study proposes a more correct approach to ecotoxicity assessment of fertilized soils for biofertilizer evaluation and demonstrates the long-term safe application of HSTAD digestate on agricultural soil.

Cr(VI) reduction capability of humic acid extracted from the organic component of municipal solid waste.

The capacity of humic acid extracted from organic waste (HAw) to reduce Cr(VI) was tested at pH 2.5, 4 and 6 and compared with coal-derived humic acid (HAc). HAw was more effective than HAc in reducing Cr(VI). The kinetics of Cr(VI) reductions depended strongly on pH. The calculation of the apparent rate coefficients indicated that HAw was more efficient at reducing Cr(VI) than HAc, but was also more efficient than HAs from soil and peat. The reduction capability of HAs depends on the type of functional groups (i.e., thiols and phenols) present, rather than the free radicals. HAw was more efficient at reducing Cr(VI) than HAc because more reactive phenols were present, i.e., methoxy- and methyl-phenols.

Influence of feedstock source on the development of polyhydroxyalkanoates-producing mixed microbial cultures in continuously stirred tank reactors.

Polyhydroxyalkanoates (PHAs) are the new frontier of bioplastic production; however, research is needed to develop and characterise efficient mixed microbial communities (MMCs) for their application with a multi-feedstock approach. Here, the performance and composition of six MMCs developed from the same inoculum on different feedstocks were investigated through Illumina sequencing to understand community development and identify possible redundancies in terms of genera and PHA metabolism. High PHA production efficiencies (>80% mg CODPHA mg-1 CODOA-consumed) were seen across all samples, but differences in the organic acids (OAs) composition led to different ratios of the monomers poly(3-hydroxybutyrate) (3HB) to poly(3-hydroxyvalerate) (3HV). Communities differed across all feedstocks, with enrichments in specific PHA-producing genera, but analysis of potential enzymatic activity identified a certain degree of functional redundancy, possibly leading to the general high efficiency seen in PHA production from all feedstocks. Leading PHAs producers across all feedstocks were identified in genera such as Thauera, Leadbetterella, Neomegalonema and Amaricoccus.

Measuring the environmental impacts of sewage sludge use in agriculture in comparison with the incineration alternative.

This study compares two scenarios for sewage sludge treatment i.e., agricultural-land application (LA) and incineration (INC), in an Italian context (Pavia province, Po Valley). The study was realised within a regional project aiming to obtain useful data to better address future sludge management policies. To do so, an attributional Life Cycle Assessment (LCA) approach was chosen and the multi-functionality was addressed by using system expansion. Results indicated that the scenario INC had higher impacts than scenario LA for the categories linked to process inputs and to the direct emissions of incineration, such as Global warming potential (= + 60 %)., Stratospheric Ozone Depletion, Ozone Formation, Mineral Resource Scarcity and Fossil Resource Scarcity. System expansion i.e., the production of non-renewable fertilisers, played a large role (higher impacts) in the categories related to resource scarcity in the INC scenario. On the other hand, LA scenario showed higher impacts than INC for direct emissions due to fertilisation (Marine and Freshwater Eutrophication, and Particulate Matter). In conclusion, the use of sewage sludge in agriculture seemed to be competitive with the alternative of incineration but both sludge quality and emission reduction during sludge distribution in the field play an important role in the reduction of environmental impacts.

Microbial community acclimatization enhances bioplastics biodegradation and biogas production under thermophilic anaerobic digestion.

This paper reports the results of a novel study of microbial acclimatization for bioplastics anaerobic degradation and conversion into biogas. Three sequential anaerobic digestion (AD) runs were carried out to favour microbial acclimatization to two different bioplastics, starch-based (SBS) and polyactic-acid (PLA). AD of SBS and PLA bioplastics was favoured by the acclimatization of the inoculum to the substrate after each run of AD. SBS conversion into biogas increased by 52 % (from 94 to 143 NL kgVS-1) and it was correlated with the enhanced growth of starch degrading bacteria such as Hydrogenispora, Halocella and Haloplasma. PLA anaerobic degradation increased by 97 % (from 395 to 779 NLbiogas kgVS-1) and it was related to the acclimatization of known PLA-degraders such as Tepidimicrobium, Methanothermobacter and Tepidanaerobacter. Microbial acclimatization appears a suitable and low-cost strategy to enhance bioplastics circularity by promoting their anaerobic biodegradation and conversion into biogas.

Pig Slurry Management Producing N Mineral Concentrates: A Full-Scale Case Study.

Manure treatment to recover nutrients presents a great challenge to delocalize nutrients from overloaded areas to those needing such nutrients. To do this, approaches for the treatment of manure have been proposed, and currently, they are mostly under investigation before being upgraded to full scale. There are very few fully operating plants recovering nutrients and, therefore, very few data on which to base environmental and economic studies. In this work, a treatment plant carrying out full-scale membrane technology to treat manure to reduce its total volume and produce a nutrient-rich fraction, i.e., the concentrate, was studied. The concentrate fraction allowed the recovery of 46% of total N and 43% of total P. The high mineral N content, i.e., N-NH4/total-N > 91%, allowed matching the REcovered Nitrogen from manURE (RENURE) criteria proposed by the European Commission to allow the potential substitution of synthetic chemical fertilizers in vulnerable areas characterized by nutrient overloading. Life cycle assessment (LCA) performed by using full-scale data indicated that nutrient recovery by the process studied, when compared with the production of synthetic mineral fertilizers, had a lower impact for the 12 categories studied. LCA also suggested precautions which might reduce environmental impacts even more, i.e., covering the slurry to reduce NH3, N2O, and CH4 emissions and reducing energy consumption by promoting renewable production. The system studied presented a total cost of 4.3 € tons-1 of slurry treated, which is relatively low compared to other similar technologies.

Nitrogen dynamics in soils fertilized with digestate and mineral fertilizers: A full field approach.

Highly stabilized digestate from sewage sludge and digestate-derived ammonium sulphate (RFs), were used in a comparison with synthetic mineral fertilizers (SF) to crop maize in a three-year plot trial in open fields. RFs and SF were dosed to ensure the same amount of mineral N (ammonia-N). In doing so, plots fertilized with digestate received much more N (+185 kg ha-1 of organic N) because digestate also contained organic N. The fate of nitrogen was studied by measuring mineral and organic N in soil at different depths, ammonia and N2O emissions, and N uptake in crops. Soil analyses indicated that at one-meter depth there was no significant difference in nitrate content between RF, SF and Unfertilized plots during crop season indicating that more N dosed with digestate did not lead to extra nitrate leaching. Ammonia emissions and N content in plants and grains measured were also similar for both RF and SF. Measuring denitrification activity by using gene makers resulted in a higher denitrification activity for RF than SF. Nevertheless, N2O measurements showed that SF emitted more N2O than RF (although it was not statistically different) (7.59 ± 3.2 kgN ha-1 for RF and 10.3 ± 6.8 kgN ha-1 for SF), suggesting that probably the addition of organic matter with digestate to RF, increased the denitrification efficiency so that N2 production was favoured. Soil analyses, although were not able detecting N differences between SF and Rf after three years of cropping, revealed a statistical increasing of total carbon, suggesting that dosing digestate lead to carbon (and maybe N) accumulation in soil. Data seem to suggest that N2O/N2 emission and organic N accumulation in soil can explain the fate of the extra N dosed (organic-N) in RF plots.

Impact of photobioreactor design on microalgae-bacteria communities grown on wastewater: Differences between thin-layer cascade and thin-layer raceway ponds.

Thin-layer (TL) photobioreactors (PBRs) are characterised by high productivity. However, their use is limited to lab/pilot-scale, and a deeper level of characterisation is needed to reach industrial scale and test the resistance of multiple microalgae. Here, the performance and composition of eight microalgal communities cultivated in the two main TLs design (thin-layer cascade (TLC) and thin-layer raceway pond (RW)) were investigated through Illumina sequencing. Chlorella vulgaris showed robustness in both designs and often acted as an "invasive" species. Inoculum and reactor type brought variability. Eukaryotic microalgae inocula led to a more robust and stable community (higher similarity), however, RWs were characterised by a higher variability and did not favour the eukaryotic microalgae. The only cyanobacterial inoculum, Nostoc piscinale, was maintained, however the community was variable between designs. The reactor design had an effect on the N cycle with the TLC and RW configurations, enhancing nitrification and denitrification respectively.

Effects of the application of microbiologically activated bio-based fertilizers derived from manures on tomato plants and their rhizospheric communities.

Bio-based fertilizers (BBFs) recovered from animal manure are promising products to optimise resources recovery and generate high agricultural yields. However, their fertilization value may be limited and it is necessary to enrich BBFs with microbial consortia to enhance their fertilization value. Three specific microbial consortia were developed according to the characteristics of three different BBFs produced from manure (bio-dried solid fraction, solid fraction of digestate and biochar) to enhance plant growth and product quality. A greenhouse pot experiment was carried out with tomato plants grown with microbiologically activated BBFs applied either as N-organic fertilizers or as an organic amendment. A next generation sequencing analysis was used to characterise the development of each rhizospheric community. All the activated BBFs gave enhanced tomato yields (fresh and dry weight) compared with the non-activated treatments and similar to, or higher than, chemical fertilization. Concerning the tomato fruits' organoleptic quality, lycopene and carotenoids concentrations were improved by biological activation. Metagenomic analysis points at Trichoderma as the main driver of the positive effects, with the effects of added bacteria being negligible or limited at the early stages after fertilization. In the context of the circular economy, the activated BBFs could be used to replace synthetic fertilisers, reducing costs and environmental burdens and increasing production.

Two-stage vs single-stage thermophilic anaerobic digestion: comparison of energy production and biodegradation efficiencies.

Two-stage anaerobic digestion (AD) for integrated biohydrogen and biomethane production from organic materials has been reported to promise higher process efficiency and energy recoveries as compared to traditional one-stage AD. This work presents a comparison between two-stage (reactors R1 and R2) and one-stage (reactor R3) AD systems, fed with identical organic substrates and loading rates, focusing the attention on chemical and microbiological aspects. Contrary to previous experiences, no significant differences in overall energy recovery were found for the two-stage and one-stage AD systems. However, an accumulation in R2 of undegraded intermediate metabolites (volatile fatty acids, ketones, amines, amino acids, and phenols) was observed by GC-MS. These compounds were thought to be both cause and effect of this partial inefficiency of the two-stage system, as confirmed also by the less diverse, and thereby less efficient, population of fermentative bacteria observed (by PCR-DGGE) in R2. The extreme environment of R1 (low pH and high metabolites concentrations) probably acted as selector of metabolic pathways, favoring H(2)-producing bacteria able to degrade such a wide variability of intermediate metabolites while limiting other strains. Therefore, if two-stage AD may potentially lead to higher energy recoveries, further efforts should be directed to ensure process efficiency and stability.

Diversifying the products from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates from the liquid fraction and biomethane from the residual solid fraction.

This study describes the diversification of products obtainable from the organic fraction of municipal solid waste (OFMSW) by producing polyhydroxyalkanoates (PHA) from the liquid fraction and biomethane from the residual solid fraction. OFMSW samples were taken during the 2021 season from two full field scale plants treating wastes. After solid/liquid (S/L) separation, 80% of initial organic acids (OAs) were released in the liquid stream. OAs were then used as feed for PHA production and residual solid cakes were tested for biomethane production. Complete mass balance and energy balance were calculated. PHAs production was of 115 ± 23 (n = 6) g kg- 1 OFMSW (TS) and residual biomethane of 219 ± 3 g kg- 1 OFMSW TS, (n = 6). Energy balance indicated that nearly 40% of OFMSW energy was recovered as products. This value was lower than that obtained previously when AD was performed before OAs separation (i.e. 64%).

Life cycle assessment of Parmigiano Reggiano PDO cheese with product environmental footprint method: A case study implementing improved slurry management strategies.

The environmental impact of Parmigiano Reggiano PDO cheese was quantified using the Product Environmental Footprint Category Rules (PEFCRs) in a Traditional System (TS) and in an Improved Management System (IMS). The TS differs from IMS with respect to slurry management (raw slurry storage vs anaerobic digestion and storage of the liquid fraction of digestate) and application of nutrients to the field (by slurry tanker with a diverter plate vs soil injection at pre-sowing and side dressing). Two additional scenarios were evaluated by considering the possible environmental enhancement achievable by reducing enteric methane production and by using soybean grain produced in Italy as the protein source for animals' diets. The environmental impact was quantified both for 1 kg of fat and protein corrected milk (FPCM) and for the production of 10 g dry matter equivalent of cheese as single score. For the first assessment, the environmental impact results were 124 and 112 µPt kg FPCM-1 for TS and IMS, respectively. In the second case, it was 10.8 µPt and 9.9 µPt 10 g dry matter equivalent-1 of cheese, for TS and IMS, respectively. The specific cost for reducing the GHG emissions in this production chain was equal to 34 € Mg-1 milk produced. Finally, although specific studies should consider the reduction of enteric methane emissions and the use of soybean grain nationally produced as feed source, the scenarios evaluated in this study highlighted some potential for environmental improvements. Even small environmental improvements to the Parmigiano Reggiano PDO cheese supply chain can bring substantial improvements to the sustainability of the food market, because of the widespread demand on the global market of Parmigiano Reggiano and of its chance of attracting consumers who are sensitive to environmental problems.

Assessing the anaerobic degradability and the potential recovery of biomethane from different biodegradable bioplastics in a full-scale approach.

The aim of the present study was to evaluate the anaerobic degradability and the potential recovery of biomethane from different bioplastics using a full-scale approach. Bioplastics were placed inside a real anaerobic digestion plant working under thermophilic conditions and quantitative and qualitative degradation of bioplastics was evaluated. Laboratory-scale experiments were used to determine the amount of biomethane produced by anaerobic degradation of bioplastics. Polylactic acid-based items may degrade completely using retention times compatible with anaerobic digestion plants contributing positively to biomethane production, i.e., in 90 days 397 ± 8 NL CH4 kgvolatile solids-1 were produced by polylactic acid-based cutlery. Starch-based shoppers showed a quick degradation of the starch component in the first month of anaerobic digestion, followed by a slow degradation of the polyester component. Anaerobic digestion and/or anaerobic digestion coupled to digestate composting may represent the best strategy to dispose these wastes meeting the principles of Circular Economy.